(1) Field of the Invention
The present invention relates to a water-soluble coolant for formation of drawn and ironed cans. More specifically, the present invention relates to a water-soluble coolant to be used for cooling and lubrication in manufacturing cans by drawing and ironing a metal blank, especially a tin-deposited steel plate, which is excellent in the cooling and lubricating actions in the drawing and ironing operation conducted at a high speed, which facilitates withdrawal of a can body formed by drawing and ironing from an ironing punch, namely, stripping of a can body, which can be washed away by water alone at the step of washing away the coolant from a can body withdrawn from the ironing punch, and which facilitates the disposal of waste water from the step of washing away the coolant.
(2) Description of the Prior Art
Drawn and ironed cans are widely used as inner pressure cans such as beer cans and carbonated drink cans because they are advantageous in that there is no seam around a can body, the entire surface can be printed, the appearance characteristics are good, the thickness of the side wall portion is small and the amount used of the metal blank can be reduced.
These drawn and ironed cans are manufactured by subjecting a shallow-drawn cup obtained by the drawing operation to ironing between an ironing punch and an ironing die several times. During this ironing operation, it is indispensable that a coolant should be supplied between the the tool and metal blank so as to obtain cooling and lubricating effects.
Aqueous emulsions comprising a mineral oil, a natural oil or fat or a synthetic oil as a base oil and a surface active agent and other additive have been used as the coolant of this type. However, these known coolants are poor in the cooling effect, are not suitable for high-speed production or improvement of the productivity and are defective in that withdrawal (stripping) of can bodies from punches are difficult when these coolants are used. Since the thickness of the side wall portion of a drawn and ironed can is extremely small, if the stripping load (applied in a direction reverse to the processing direction) is increased, buckling is caused on the top of the side wall portion and the can may not be used as a container. Moreover, since water-insoluble components are forcibly dispersed, the adaptability of the coolants to the washing operation is not easy, and therefore, an alkali degreasing step is indispensable. Moreover, a coolant comprising a lubricant of the synthetic oil type, especially a water-soluble lubricant, is defective in that the lubricant contained in waste water can hardly be separated according to a conventional coagulation sedimentation method or activated sludge method.